Dimensional inspection techniques shall be used in the fabrication process of, particularly, large composite parts, i.e. parts made out with composite materials consisting of fibers or fiber bundles embedded in a matrix of thermosetting or thermoplastic resin, such as aircraft wing covers, to assure that the dimensional and geometrical features of the fabricated part do not deviate from its nominal values by more than a predetermined amount.
Since the acceptability and reliability of a composite part can be affected if said features do not conform to design objectives, it is necessary to perform a detailed dimensional inspection in the final stage of the fabrication process.
In the prior art, the dimensional inspection of a large composite part is usually done in the curing tool using a manual laser interferometer and assuming that the curing tool surface is the nominal or theoretical composite part outer surface, i.e. the aerodynamic surface in the case of aircraft wing covers. In this respect, vacuum is used to push the composite part inner surface to the curing tool surface in order to overcome the deformations that may appear after the curing cycle. Deviations are calculated by comparing directly the distance from a number of selected points in the inner surface to the curing tool surface with the corresponding nominal distance.
However, the assumption that the curing tool surface can be used as the nominal outer surface of the composite part, as it has been seen in several tests, is erroneous: the curing tool may not follow exactly the nominal outer surface due to machining deviations and/or to level problems and the vacuum power may not be enough to overcome the stiffness of the part. Consequently the dimensional inspection results are not as accurate as is needed.
The present invention focuses on finding a solution for these drawbacks.